A Graphical User Interface (GUI) is way the players interact with your games. You've actually been using a GUI in the previous chapter (the Unity Editor) and also when interacting with your operating system. Without a GUI of some sort, the only way you'd be able to interact with a computer is a command prompt such as DOS or UNIX.

When working on GUIs, we want them to be as intuitive as possible and only contain the information that is pertinent to the player at any given time. There are people whose main job is programming and/or designing user interfaces and there are college degrees on the subject as well. So, while we won't talk about everything that we have to work with on GUIs, I do want to touch on the aspects that should be quite helpful when working on your own projects in the future.